Capacitive DEIONIZATION is not new, yet it has not had a huge commercial success due to the high cost of implementation. Another reason for the lack of commercial success is the historical problem of contamination of capacitive deionization units by organic compounds and high ionic loads both of which are alleviated by the ozonation and separation steps prior to the capacitive deionization. When these problems are eliminated, one obtains longer useful life for the equipment, reduced power consumption, and faster regeneration of the CD unit. The grandfather patent in the field is Farmer, U.S. Pat. No. 5,425,858 issued Jun. 20, 1995 to Joseph Farmer of Lawrence Livermore Laboratory, which patent is assigned to the Regents of the University of California. It is titled “Method and apparatus for capacitive deionization, electrochemical purification and regeneration of electrodes.”
It is well known throughout California and other parts of the western USA that obtaining reliable and plentiful supply of clean water is becoming more and more difficult, especially in, view of the recent drought years of 2006 and 2007 winters. Not only in the USA but in Africa, Australia and the middle east, there are huge water availability problems. For this reason Israel a little country has become a big player in the water desalination industry.
CDT Systems of Dallas Tex. has licensed the aforementioned Farmer patent as well as other Lawrence Livermore patents pertaining to the impregnation of a carbon paper support with a water-resorcinol-formaldehyde solution, and then polymerizing the resorcinol formaldehyde resin, extracting the water, and then heating the polymerized resin/paper structure to convert the resin to a micro porous carbon aerogel supported on the paper. While the original process was and still remains costly, CDT has achieved significant reductions in cost to permit wider adoption of the capacitive deionization process using carbon aerogels in specialized situations.
It is also known to the art that high sodium ion content is detrimental to agriculture. The NaCl content when high affects the permeability of the soil by rain or other irrigation water. Sodium when present in soil tends to replace calcium and magnesium according to the periodic table from the soil and the sodium causes dispersion of soil particles thus reducing the ease of cultivation and permeability of the soil to permit moisture to seep down to plant roots. The soil becomes hard and compact. Other known problems caused by excess sodium in irrigation water include formation of crusted seed beds, short term saturation of the surface soil, while water fails to sink down to root hairs. The pH goes up and this may be bothersome or evenly deadly to some plants.
In the USA, Australia and England and other countries, there is much coal produced, most of which is used for power generation. Coal bed methane exists in areas where the dominant chemistry of the water in a coal seam is sodium bicarbonate and where the coal seam is buried deeply enough to maintain sufficient water pressure to hold the gas in place. Since Coal Bed Methane hereinafter CBM travels with ground water in coal seams, extraction of CBM for commercial use involves pumping available water from the seam in order to reduce the water pressure that holds gas in the seam. CBM has very low solubility in water and readily separates as pressure decreases, allowing it to be piped out of the well separately from the water. Water moving from the coal seam to the well bore encourages gas migration toward the well. But the capture of this methane gas creates a lot of water that is unsuitable for agriculture or other domestic uses. This water which is known as coal bed methane gas water, is also known by the term, PRODUCED WATER, and it must be purified before it can used. CBM water also contains a high amount of salinity, and since people don't like the taste of salt water, even if the water is pure from microbes and other toxics, the salt content must be reduced or eliminated. Not only is the high sodium content a taste problem, it is also a health problem when ingested in large quantities. Salt water's only domestic use is as a gargle, for sore throats But this is more than a taste issue, it is a health issue. Soil destruction also takes place due to the SAR effect.
But why is this purified high salinity water unsuitable for agricultural purposes?
Salinity becomes a problem when enough salts accumulate in the root zone to negatively affect plant growth. Excess salts in the root zone hinder plant roots from withdrawing water from surrounding soil. This lowers the amount of water available to the plant, regardless of the amount of water actually in the root zone. For example, when plant growth is compared in two identical soils with the same moisture levels, one soil receiving salty water and the other receiving salt-free water, plants are able to use more water from the soil receiving salt-free water. Although the water is not held tighter to the soil in saline environments, the presence of salt in the water causes plants to exert more energy extracting water from the soil. The main point is that excess salinity in soil water can decrease plant available water and cause plant stress.
One very specific application of the process of this invention relates to the generation of water suitable for both domestic and agricultural purposes from coal bed methane gas water by a specialized form of capacitive deionization followed by possible further treatment to reduce the salinity. Not only is the water ultimately produced by this process suitable for agriculture but it is suitable for human consumption as well.